A large RSV vaccine study using a Praxis Biologics, formalin-inactivated (FI) RSV vaccine was conducted. Twenty-one seronegative rhesus were divided into seven groups of three monkeys each. Four groups (Gp) received IM injections of the FI-RSV vaccine, ranging from high (250ul) to low (50ul of a 1:25 dilution), in five-fold dilutions, while Gp 5 received the Praxis prepared FI-sham vaccine. An independently prepared, Prince FI-RSV vaccine was used to inoculate Gp6, IM. Finally, Gp 7 was intranasally infected with live RSV. Twenty-one days later, a booster vaccine was administered to the first six groups. Finally, on day 56 post inoculation, a live RSV challenge was administered to all 21 animals. The high dose vaccine group had the greatest antibody response to vaccine and the lowest level of virus in both the upper and lower respiratory tract, and indicated a dose effect of the vaccine in these animals. As expected, the reinfection group was protected on challenge. Flow cytometry of bronchoalveolar samples showed a three-four fold increase in the B lymphocyte population in the lungs of the FI-RSV vaccine recipients following RSV challenge, compared with the sham vaccine and the reinfection groups. Conversely, these two latter groups demonstrated an increase in T cells, specificially CD8+ T cells. On day 8 post challenge, the animals were necropsied. Sections from each of the lung lobes were harvested and scored for lesions, by histopathology. Both Praxis and Prince vaccines resulted in increased lung scores over that of the reinfection group, suggesting a distinct immunopotentiation. These animals had a neutrophilic infiltration, predominately of eosinophils, along with some elevation in IL4 and IL5 levels, suggesting their role in the pathology of the disease. The lung scores, eosinophils and cytokine levels of the control FI-sham vaccine animals, however, were as high as the experimental animals and suggested the vaccine was not a true sham as thought. The preparation of this control is under investigation. FUNDING NIH RO1 AI 37197-04, $135,800, UAB subcontract PUBLICATIONS None